An important precursor of my novel method is the disc diffusion test that is known in the microbiological art as the Kirby-Bauer test. In this method a filter paper disc impregnated with a chemical is placed on agar so that, with or without incubation, the chemical in the disc will diffuse from the disc into the agar. If a susceptible organism is placed in or on the agar, it will not grow in the area surrounding the disc if the organism is susceptible to the chemical, and this lack of growth is visually apparent. The area around the disc created by the lack of growth is known as the zone of inhibition.
The Kirby-Bauer method has been used to test the effectiveness of a variety of antibiotics against various pathogens. Many factors are considered in testing effectiveness, e.g., the agar utilized, the depth of the agar, the quantity of organisms in the agar, and the conditions of incubation, which are maintained as a constant. Under these conditions, the zone of inhibition will be the only variable, and the greater the zone, the more effective will be the antibiotic. The size of the zone of a particular antimicrobial may also be influenced by the diffusion capability of the substance.
While the Kirby-Bauer disc diffusion test has, to the best of my knowledge, previously found primary use in the determination of antimicrobial properties of various materials, it can also be more broadly used. Thus, while the indicator that is dispersed in the agar or another gel is usually a bacterium, the indicator can be other living organisms such as yeast, plantlets, seeds, algae, or chemicals that cause an opalescence in the gel, such as an oil, fat, cellulose, starch, etc. When the material that has been impregnated into the disc is applied to the gel or agar, a halo of change in the gel will indicate a zone of activity of the impregnated material. With specific respect to a determination of antibiotic activity, after incubation a clear halo about the disc will indicate the extent of activity of the antibiotic impregnated in the disc.